Optical switch incorporating stepped faceted mirrors

ABSTRACT

An optical switch that includes optical paths organized into a set of M input optical paths and a set of N output optical paths. The optical switch additionally includes a faceted mirror corresponding to each of the M input optical paths and including N facets and a faceted mirror corresponding to each of the N output optical paths and including M facets. Finally, the optical switch includes a moving mechanism coupled to each faceted mirror to step the faceted mirror to selectively align one of the facets of the faceted mirror with the one of the optical paths with which the faceted mirror is associated. The facets of each of the faceted mirrors corresponding to one of the sets of optical paths, i.e., the set of input optical paths or the set of output optical paths, are preferably angled to reflect light towards a different one of the faceted mirrors corresponding to the other of the sets of optical paths, i.e., the set of output optical paths or the set of input optical paths, respectively.

FIELD OF THE INVENTION

[0001] The invention relates to optical switches and, in particular, toan M×N optical switch in which the optical signals are switched usingstepped, faceted mirrors.

BACKGROUND OF THE INVENTION

[0002] MEMS-based M×N optical switches are currently being developed foruse in optical switching systems, such as the optical switching systemsused to switch optical signals from one optical fibre to another in anoptical network. In such an optical switch, an optical signal receivedvia an input fibre illuminates a first steerable mirror. The input fibreis one of M input fibres. The first steerable mirror is associated withthe input fibre and steers the optical signal towards a second steerablemirror. The second steerable mirror is associated with an output fibre.The output fibre is one of N output fibres. The second steerable mirrorreflects the optical signal received from the first steerable mirrorinto the output fibre.

[0003] In such an optical switch, the angle of each of the steerablemirrors must be accurately set to a precision in the order of 1 part in2¹³ to couple the optical signal from the input fibre to the outputfibre with a high coupling efficiency. When the input and output fibresare arrayed in two-dimensional arrays, the angle of the steerablemirrors must be set with the required precision about each of twoorthogonal axes. Complex, closed-loop positioning mechanisms arerequired to achieve this accuracy.

SUMMARY OF THE INVENTION

[0004] The invention provides an optical switch comprising optical pathsorganized into a set of M input optical paths and a set of N outputoptical paths. The optical switch additionally comprises a facetedmirror corresponding to each of the M input optical paths and includingN facets and a faceted mirror corresponding to each of the N outputoptical paths and including M facets. Finally, the optical switchcomprises a moving mechanism coupled to each faceted mirror to step thefaceted mirror to selectively align one of the facets of the facetedmirror with the one of the optical paths with which the faceted mirroris associated.

[0005] The facets of each of the faceted mirrors corresponding to one ofthe sets of optical paths, i.e., the set of input optical paths or theset of output optical paths, are angled to reflect light towards adifferent one of the faceted mirrors corresponding to the other of thesets of optical paths, i.e., the set of output optical paths or the setof input optical paths, respectively.

[0006] The optical switch according to the invention avoids the need toset the angle of steerable mirrors with great accuracy by replacing eachof the steerable mirrors of the conventional MEMS-based optical switchwith a stepped, faceted mirror. Each facet of the mirror is fabricatedwith the required angular precision, but the mirror is simply steppedlinearly in one or two directions, or rotationally, to align theappropriate facet of the faceted mirror with the input optical path orthe output optical path. The precision with which the mirror needs to bestepped is substantially less than that with which the angles of thesteerable mirrors need to be set. This simplifies and reduces the costof making the optical switch according to the invention. Moreover, thesteps with which each of the mirrors is moved can be made equal to oneanother. This enables a simple electrostatic stepper motor to be used asthe moving mechanism, which further simplifies and reduces the cost ofthe optical switch according to the invention compared with aconventional optical switch.

[0007] The invention additionally provides a method for switching anoptical signal received via an input optical path to an output opticalpath. The input optical path is any one of an array of M input opticalpaths and the output optical path is any one of an array of N outputoptical paths. In the method, an N-faceted mirror corresponding to eachof the M input optical paths and an M-faceted mirror corresponding toeach of the N output optical paths are provided. Each N-faceted mirroris located opposite the corresponding one of the input optical paths.Each M-faceted mirror is located opposite the corresponding one of theoutput optical paths. The N-faceted mirror corresponding to the inputoptical path is stepped to align one of the facets thereof with theinput optical path. The facet aligned with the input optical path isangled to reflect the optical signal towards the M-faceted mirrorcorresponding to the output optical path. The M-faceted mirrorcorresponding to the output optical path is stepped to align one of thefacets thereof with the output optical path. The facet aligned with theoutput optical path is angled to reflect light that would be receivedvia the output optical path towards the N-faceted mirror correspondingto the input optical path.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a schematic diagram showing a simplified firstembodiment of an optical switch according to the invention. The opticalswitch is shown configured to switch an optical signal from the inputoptical path 20 to the output optical path 32.

[0009]FIG. 2A is an enlarged schematic side view of a first embodimentof an exemplary one of the faceted mirrors of the optical switch shownin FIG. 1.

[0010]FIG. 2B is an enlarged schematic side view of a second embodimentof an exemplary one of the faceted mirrors of the optical switch shownin FIG. 1.

[0011]FIG. 3A is a schematic diagram showing the simplified embodimentof the optical switch shown in FIG. 1 reconfigured to switch an opticalsignal from the input optical path 20 to the output optical path 30.

[0012]FIG. 3B is a schematic diagram showing the simplified embodimentof the optical switch shown in FIG. 1 reconfigured to switch an opticalsignal from the input optical path 20 to the output optical path 31.

[0013]FIG. 3C is a schematic diagram showing the simplified embodimentof the optical switch shown in FIG. 1 reconfigured to switch an opticalsignal from the input optical path 20 to the output optical path 33.

[0014]FIG. 4A is a schematic diagram showing the simplified embodimentof the optical switch according to the invention partially reconfiguredto switch an optical signal from the input optical path 21 to the outputoptical path 32.

[0015]FIG. 4B is a schematic diagram showing the simplified embodimentof the optical switch according to the invention fully reconfigured toswitch the optical signal from the input optical path 21 to the outputoptical path 32.

[0016]FIG. 5 is a schematic diagram showing a simplified secondembodiment of an optical switch according to the invention.

[0017]FIGS. 6A and 6B are enlarged schematic elevation and plan views ofan embodiment of an exemplary one of the faceted mirrors of the opticalswitch shown in FIG. 5.

[0018]FIG. 7 is a schematic diagram showing a simplified thirdembodiment of an optical switch according to the invention. The opticalswitch is shown configured to switch an optical signal from the inputoptical path 20 to the output optical path 32.

[0019]FIG. 8A is a schematic diagram showing the simplified embodimentof the optical switch shown in FIG. 7 reconfigured to switch an opticalsignal from the input optical path 20 to the output optical path 30.

[0020]FIG. 8B is a schematic diagram showing the simplified embodimentof the optical switch shown in FIG. 7 reconfigured to switch an opticalsignal from the input optical path 20 to the output optical path 31.

[0021]FIG. 8C is a schematic diagram showing the simplified embodimentof the optical switch shown in FIG. 7 reconfigured to switch an opticalsignal from the input optical path 20 to the output optical path 33.

[0022]FIG. 9 is a flow diagram illustrating the method according to theinvention for switching an optical signal.

DETAILED DESCRIPTION OF THE INVENTION

[0023]FIG. 1 shows a simplified first embodiment 10 of an optical switchaccording to the invention. The optical switch is composed of the set 12of M input optical paths, the set 14 of N output optical paths, afaceted mirror corresponding to each of the M input optical paths andhaving N facets, a faceted mirror corresponding to each of the N outputoptical paths and having M facets, and a moving mechanism coupled toeach faceted mirror to linearly step the faceted mirror to align one ofthe facets of the faceted mirror with the optical path to which thefaceted mirror corresponds.

[0024] In the example shown in FIG. 1, the set 12 of input optical pathsis composed of the three input optical fibres 20, 21 and 22 arranged asa one-dimensional array disposed in the x-direction, and the set 14 ofoutput optical paths is composed of the four output fibres 30, 31, 32and 33 also arranged in a one-dimensional array disposed in thex-direction. The set 13 of output optical paths is located opposite theset 12 of input optical paths in the same plane, and is offset from theset of input optical paths in the x-direction and in the y-direction.Locating the output optical paths and the input optical paths in thesame plane simplifies the design of the faceted mirrors, but is notessential to the invention.

[0025] Located opposite the light-emitting ends of the input fibres 20,21 and 22 are the faceted mirrors 40, 41 and 42 respectively. Each ofthe faceted mirrors is located to receive light from a different one ofthe input fibres, and is said to correspond to the input fibre. In theexample shown, the set 14 of output optical paths is composed of fouroptical fibres, so the faceted mirrors 40-42 each have four facets.

[0026] Located opposite the ends of the output fibres 30, 31, 32 and 33are the faceted mirrors 50, 51, 52 and 53, respectively. Each of thefaceted mirrors is located in a position at which it would receive lightfrom a different one of the output fibres if light were output from theoutput fibres, and is said to correspond to the output fibre. In theexample shown, the set 12 of input optical paths is composed of threeoptical fibres, so the faceted mirrors 50-53 each have three facets.

[0027] The number of facets stated above are minimum numbers. It may bedesirable for the faceted mirrors to have more than the minimum numberof facets stated above. For example, when the number of input opticalpaths differs from the number of output optical paths, providing thefaceted mirrors corresponding to the larger set of optical paths withthe same number of facets as the faceted mirrors corresponding to thesmaller set of optical paths allows the same mirror design to be used incorresponding positions with both the output optical paths and the inputoptical paths. This would also allow the numbers of input optical pathsor output optical paths to be increased later, for example. However,facets in excess of the minimum numbers stated above will be unused.

[0028] The fibres constituting the set 12 of input optical paths and theset 13 of output optical paths, the faceted mirrors 40-42 and thefaceted mirrors 50-53 are mounted on a suitable armature (not shown)that precisely defines their positions relative to one another.

[0029]FIG. 2A is an enlarged view of a first embodiment of the facetedmirror 40 shown in FIG. 1. The faceted mirror is composed of the stage60 on which are mounted the four mirror facets 61, 62, 63 and 64arranged in a one-dimensional array disposed in the x-direction. Thestage is movably mounted on the stator 67 in a manner that allows thestage to move freely in the x-direction, but which constrains the stagefrom moving in the y- and z-directions. For example, high aspect ratiobendable flexures (not shown) may extend between the stage and thestator to allow the stage to move freely in the x-direction but torestrain movement of the stage in the y- and z-directions.

[0030] The faceted mirrors 41 and 42 are similarly configured to thefaceted mirror 40 and are similarly mounted on the stage 67. The facetedmirrors 50-53 are also similarly configured and are similarly mounted onthe stator 68.

[0031] Disposed between the stage 60 and the stator 67 is the movingmechanism shown schematically at 70. The moving mechanism moves thestage 60, and, hence, the mirror facets 61-64, back and forth in thex-direction, as indicated by the arrows 69. The moving mechanism ispreferably a precision linear electrostatic or electromagnetic steppermotor that moves the stage in the x-direction between predeterminedpositions. At each of the predetermined positions, a different one ofthe mirror facets 61-64 is aligned with the light output by the inputoptical path 20. A precision linear electrostatic stepping motor of thetype described in U.S. Pat. No. 5,986,381 of Hoen et al. is preferred.The centers of the mirror facets are preferably equally spaced in thex-direction to make the distances between the predetermined positionsequal. The electrodes of the Hoen stepping motor can then be fabricatedwith a pitch that enables the stepping motor to move the stageautomatically and precisely to each of the predetermined positions.

[0032] Alternatively, the moving mechanism 70 can comprise a rotarymotor, preferably a rotary stepper motor, and a suitable transmissionthat converts rotary motion into linear motion. As further alternatives,piezoelectric actuators or piezoelectric benders or other precisionmechanisms that generate linear movement can be used. Such mechanismscan be used with or without feedback control of the position of thestage 60.

[0033] The faceted mirrors 41, 42 and 50-53 are each equipped with amoving mechanism similar to the moving mechanism 70.

[0034] The mirror facets 61-64 of the faceted mirror 40 are angleddifferently from one another such that each of them reflects lightreceived from the input fibre 20 towards a different one of the facetedmirrors 50-53 corresponding to the set 14 of output optical paths. Inparticular, the mirror facets 61, 62, 63 and 64 are angled such thatthey reflect light received from the input optical path 20 to towardsthe faceted mirrors 50, 51, 52 and 53, respectively, corresponding tothe output fibres 31, 32, 33 and 34, respectively.

[0035] The mirror facets of the faceted mirrors 41 and 42 are alsoangled to meet the conditions as those just described. However, sincethe positions in the x-direction of the input fibres 21 and 22corresponding to the faceted mirrors 41 and 42, respectively, differfrom one another and from that of the input fibre 20, the angles of themirror facets of the faceted mirrors 41 and 42 differ from one anotherand from those of the mirror facets of the faceted mirror 40.

[0036] The mirror facets of the faceted mirrors 50-53 corresponding tothe set 14 of output optical paths are angled such that, if light wereoutput by the output fibres 30-33, each mirror facet would reflect suchlight towards on a different one of the faceted mirrors 40-42,respectively, corresponding to the set 12 of input optical paths. Whenangled to meet the condition just described, each facet of the facetedmirrors 50-53 reflects light received from a different one of thefaceted mirrors 40-42 into the output optical path corresponding to thefaceted mirror.

[0037]FIG. 1 shows an example in which the optical switch 10 isconfigured to switch an optical signal from the input fibre 20 to theoutput fibre 32. The moving mechanism 70 linearly steps the facetedmirror 40 in the x-direction to align the facet 63 with the input fibre20. The facet 63 reflects the optical signal received from the inputfibre 20 towards the faceted mirror 52 corresponding to the output fibre32 in the set 14 of output optical paths.

[0038] The moving mechanism 82 coupled to the faceted mirror 52 linearlysteps the moving mirror in the x-direction to align the facet 91 withthe output fibre 32. The optical signal received via the input fibre 20and reflected by the faceted mirror 40 is incident on the facet 91 ofthe faceted mirror 52. The facet 91 is angled such that it reflects theoptical signal into the output optical path 32.

[0039]FIG. 3A shows an example in which the optical switch 10 isreconfigured to switch the optical signal from the input fibre 20 to theoutput fibre 30. The moving mechanism 70 has linearly stepped thefaceted mirror 40 in the x-direction to align the facet 61 with theinput fibre 20. The moving mechanism 80 has linearly stepped the facetedmirror 50, which corresponds to the output fibre 30, in the x-directionto align the facet 92 with the output fibre 30.

[0040] The facet 61 of the faceted mirror 40 reflects the optical signaloutput by the input fibre 20 towards the faceted mirror 50. At thefaceted mirror 50, the optical signal is incident on the facet 92, whichis angled to reflect the optical signal into the output fibre 30.

[0041]FIG. 3B shows an example in which the optical switch 10 isreconfigured to switch the optical signal from the input fibre 20 to theoutput fibre 31. The moving mechanism 70 has linearly stepped thefaceted mirror 40 in the x-direction to align the facet 62 with theinput fibre 20. The moving mechanism 81 has linearly stepped the facetedmirror 51, which corresponds to the output fibre 31, in the x-directionto align the facet 93 with the output fibre 31.

[0042] The facet 62 of the faceted mirror 40 reflects the optical signaloutput by the input fibre 20 towards towards the faceted mirror 51. Atthe faceted mirror 51, the optical signal is incident on the facet 93,which is angled to reflect the optical signal into the output fibre 31.

[0043]FIG. 3C shows an example in which the optical switch 10 isreconfigured to switch the optical signal from the input fibre 20 to theoutput fibre 33. The moving mechanism 70 has linearly stepped thefaceted mirror 40 in the x-direction to align the facet 64 of thefaceted mirror 40 with the input fibre 20. The moving mechanism 83 haslinearly stepped the faceted mirror 53, which corresponds to the outputfibre 33, in the x-direction to align the facet 94 with the output fibre33.

[0044] The facet 64 of the faceted mirror 40 reflects the optical signaloutput by the input fibre 20 towards the faceted mirror 53. At thefaceted mirror 53, the optical signal is incident on the facet 94, whichis angled to reflect the optical signal into the output fibre 33.

[0045]FIG. 4A shows an example in which the optical switch 10 ispart-way through being configured from the state shown in FIG. 1 toswitch an optical signal from the input fibre 21 to the output fibre 32.The moving mechanism 71 of the faceted mirror 41, corresponding to theinput fibre 21, has linearly stepped the faceted mirror 41 in thex-direction to align the facet 95 with the input fibre 21. The facet 95reflects the optical signal received via the input fibre 21 towards thefaceted mirror 52 that corresponds to the output fibre 32. However, theoptical signal is incident on the facet 91 of the faceted mirror 52 at adifferent angle of incidence from that of the optical signal shown inFIG. 1 as being received via the input fibre 20. Thus, the facet 91reflects the optical signal received via the input fibre 21 with anangle of reflection that results in the optical signal missing theoutput fibre 32.

[0046]FIG. 4B shows the optical switch 10 fully reconfigured to switchthe optical signal from the input fibre 21 to the output fibre 32. Themoving mechanism 82 has linearly stepped the faceted mirror 52 in the−x-direction to align the facet 96 with the output optical path 32. Thefacet 96 is angled to reflect the optical signal received from the facet95 of the faceted mirror 41 into the output fibre 32.

[0047] It will be apparent to a person of ordinary skill in the art thatthe optical switch 10 may be reconfigured by laterally stepping variousones of the faceted mirrors 40-42 and 50-53 to switch an optical signalreceived via any one of the M input fibres to any one of the N outputfibres in a manner similar to the switching operations exemplified inFIGS. 3A-3C, 4A and 4B. It will also be apparent to the person ofordinary skill in the art that the simplified embodiments shown in thisdisclosure can easily be extended to operates with larger arrays ofinput fibres and output fibres and correspondingly larger arrays offaceted mirrors, each faceted mirror having a correspondingly largernumber of facets.

[0048]FIG. 5 shows a simplified second embodiment 150 of an opticalswitch according to the invention. Elements of the embodiment 150 thatcorrespond to elements of the embodiment 10 shown in FIG. 1 areindicated by the same reference numerals and will not be described againhere. The optical switch is composed of the set 12 of M input opticalpaths, the set 14 of N output optical paths, a faceted mirrorcorresponding to each of the M input optical paths and having N facets,a faceted mirror corresponding to each of the N output optical paths andhaving M facets, and a moving mechanism coupled to each faceted mirrorto rotationally step the faceted mirror to align one of the facets ofthe faceted mirror with the optical path to which the faceted mirrorcorresponds.

[0049] Located opposite the light-emitting ends of the input fibres 20,21 and 22 are the faceted mirrors 140, 141 and 142 respectively. Each ofthe faceted mirrors is located to receive light from a different one ofthe input fibres, and is said to correspond to the input fibre. In theexample shown, the set 14 of output optical paths is composed of fouroptical fibres, so the faceted mirrors 140-142 each have four facets.

[0050] Located opposite the ends of the output fibres 30, 31, 32 and 33are the faceted mirrors 150, 151, 152 and 153, respectively. Each of thefaceted mirrors is located in a position at which it would receive lightfrom a different one of the output fibres if light were fed into theoutput fibres, and is said to correspond to the output fibre. In theexample shown, the set 12 of input optical paths is composed of threeoptical fibres, so the faceted mirrors 150-153 each have three facets.

[0051] The number of facets stated above are minimum numbers, as notedabove.

[0052]FIGS. 6A and 6B are enlarged elevation and plan views of anembodiment of the faceted mirror 140 of the optical switch 150 shown inFIG. 5. The faceted mirror is composed of the stage 160 on which aremounted the four mirror facets 61, 62, 63 and 64. The stage isrotationally mounted on the pivot 68 affixed to the stator 67 in amanner that allows the stage to rotate freely between predeterminedangular positions, but which constrains lateral movement of the stage.The faceted mirrors 141 and 142 are similarly configured and aresimilarly mounted on the stator 67. The faceted mirrors 150-153 aresimilarly configured and are similarly pivotally mounted on the stator168.

[0053] Disposed between the stage 60 and the stator 67 is the movingmechanism shown schematically at 170. The moving mechanism moves thestage 60, and, hence, the mirror facets 61-64, rotationally about thepivot 68, as indicated by the arrows 169. The moving mechanism ispreferably a precision rotary electrostatic or electromagnetic steppermotor that rotates the stage about the pivot between predeterminedrotational positions. At each of the predetermined rotational positions,a different one of the mirror facets 61-64 is aligned with the lightoutput by the input optical path 20. A precision rotary electrostaticstepping motor of the type described in U.S. Pat. No. 5,986,381 of Hoenet al. is preferred. The centers of the mirror facets are preferablyspaced at equal angles about the pivot to make the angles between thepredetermined rotational positions equal. The electrodes of the Hoenrotary stepping motor can then be fabricated with a pitch that enablesthe stepping motor to move the stage automatically and precisely to eachof the predetermined rotational positions.

[0054] Alternatively, the moving mechanism 170 can comprise anelectromagnetic rotary motor, preferably a rotary stepper motor. Asfurther alternatives, piezoelectric actuators or piezoelectric benders,and a suitable transmission that converts linear motion into rotarymotion or other precision mechanisms that generate rotary movement canbe used. Such mechanisms can be used with or without feedback control ofthe rotational position of the stage 160. Such mechanisms can be usedwith or without a mechanical detent that defines the predeterminedrotational positions.

[0055] The faceted mirrors 41, 42 and 50-53 are each equipped with arotational moving mechanism similar to the moving mechanism 170.

[0056] The facets of each of the faceted mirrors corresponding to one ofthe sets of the optical paths are angled to reflect light towards adifferent one of the faceted mirrors corresponding to the other of thesets of the optical paths, as described above.

[0057]FIG. 5 shows an example in which the optical switch 150 isconfigured to switch an optical signal from the input fibre 20 to theoutput fibre 32. The moving mechanism 170 rotationally steps the facetedmirror 140 about the pivot 68 to align the facet 63 with the input fibre20. The facet 63 reflects the optical signal received from the inputfibre 20 towards the faceted mirror 152 corresponding to the outputfibre 32 in the set 14 of output optical paths.

[0058] The moving mechanism 182 coupled to the faceted mirror 152rotationally steps the moving mirror about its pivot to align the facet191 with the output fibre 32. The optical signal received via the inputfibre 20 and reflected by the faceted mirror 140 is incident on thefacet 191 of the faceted mirror 152. The facet 191 is angled such thatit reflects the optical signal into the output optical path 32.

[0059] It will be apparent to a person of ordinary skill in the art thatthe optical switch 150 may be reconfigured by rotating the appropriateones of the faceted mirrors 140-142 and 150-153 to switch an opticalsignal received via any one of the M input fibres to any one of the Noutput fibres in a manner similar to the switching operationsexemplified in FIGS. 3A-3C, 4A and 4B. It will also be apparent to theperson of ordinary skill in the art that the simplified embodimentsshown in this disclosure can easily be extended to operates with largerarrays of input fibres and output fibres and correspondingly largerarrays of rotating faceted mirrors, each faceted mirror having acorrespondingly larger number of facets.

[0060] In the embodiments of the optical switch according to theinvention shown in FIGS. 1 and 5, the set 13 of output optical paths ismounted opposite the set 12 of input optical paths, and is offset fromthe set of input optical paths in the x-direction and in they-direction. The faceted mirrors 40-42 or 140-142 are mounted oppositethe set 12 of input optical paths and offset from the set of inputoptical paths in the−y-direction. The faceted mirrors 50-52 or 150-152are mounted opposite the set 13 of output optical paths and offset fromthe set of output optical paths in the y-direction

[0061] In some applications, it may be more convenient for the inputoptical paths and the output optical paths to be located in a commonplane, and for the faceted mirrors 40-42 or 140-142 and the facetedmirrors 50-52 or 150-152 to be located in and mounted on a common plane.FIGS. 7 shows a third embodiment 200 of the optical switch according tothe invention in which the elements of the optical switch 10 shown inFIG. 1 have been rearranged to place the set 13 of input optical pathsin the same plane as the set 12 of input optical paths and offset fromthe set of input optical paths in the y-direction, and to offset thefaceted mirrors from the optical paths in the−y-direction with thefaceted mirrors 50-53 offset from the faceted mirrors 40-42 in thex-direction. The embodiment shown in FIG. 5 may be similarly rearranged.Elements of the embodiment shown in FIG. 7 that correspond to elementsof the embodiment shown in FIG. 1 are indicated by the same referencenumerals and will not be described again here.

[0062] The optical switch 200 additionally includes the common mirror 16located between the set 12 of input optical paths and the set 13 ofoutput optical paths and facing the plane in which the faceted mirrorsare located.

[0063]FIG. 7 shows an example in which the optical switch 200 isconfigured to switch an optical signal from the input fibre 20 to theoutput fibre 32. The moving mechanism 70 linearly steps the facetedmirror 40 in the x-direction to align the facet 63 with the input fibre20. The facet 63 reflects the optical signal received from the inputfibre 20 towards the point 75 on the common mirror 16. The opticalsignal is incident on point 75 of the common mirror at an angle ofincidence at which the common mirror reflects the optical signal towardsthe faceted mirror 52 corresponding to the output fibre 32 in the set 14of output optical paths.

[0064] The moving mechanism 82 coupled to the faceted mirror 52 linearlysteps the moving mirror in the x-direction to align the facet 91 withthe output fibre 32. The optical signal received via the input fibre 20and reflected by the faceted mirror 40 and point 72 of the common mirror16 is incident on the facet 91 of the faceted mirror 52. The facet 91 isangled such that it reflects the optical signal into the output opticalpath 32.

[0065]FIG. 8A shows an example in which the optical switch 200 isreconfigured to switch the optical signal from the input fibre 20 to theoutput fibre 30. The moving mechanism 70 has linearly stepped thefaceted mirror 40 in the x-direction to align the facet 61 with theinput fibre 20. The moving mechanism 80 has linearly stepped the facetedmirror 50, which corresponds to the output fibre 30, in the x-directionto align the facet 92 with the output fibre 30.

[0066] The facet 61 of the faceted mirror 40 reflects the optical signaloutput by the input fibre 20 towards the point 76 on the common mirror16. The optical signal is incident on the point 76 of the common mirrorat an angle of incidence at which the common mirror reflects the opticalsignal towards the faceted mirror 50. At the faceted mirror 50, theoptical signal reflected by the common mirror is incident on the facet92, which is angled to reflect the optical signal into the output fibre30.

[0067]FIG. 8B shows an example in which the optical switch 200 isreconfigured to switch the optical signal from the input fibre 20 to theoutput fibre 31. The moving mechanism 70 has linearly stepped thefaceted mirror 40 in the x-direction to align the facet 62 with theinput fibre 20. The moving mechanism 81 has linearly stepped the facetedmirror 51, which corresponds to the output fibre 31, in the x-directionto align the facet 93 with the output fibre 31.

[0068] The facet 62 of the faceted mirror 40 reflects the optical signaloutput by the input fibre 20 towards the point 77 on the common mirror16. The optical signal is incident on the point 77 at an angle ofincidence at which the common mirror reflects the optical signal towardsthe faceted mirror 51. At the faceted mirror 51, the optical signalreflected by the common mirror is incident on the facet 93, which isangled to reflect the optical signal into the output fibre 31.

[0069]FIG. 8C shows an example in which the optical switch 200 isreconfigured to switch the optical signal from the input fibre 20 to theoutput fibre 33. The moving mechanism 70 has linearly stepped thefaceted mirror 40 in the x-direction to align the facet 64 of thefaceted mirror 40 with the input fibre 20. The moving mechanism 83 haslinearly stepped the faceted mirror 53, which corresponds to the outputfibre 33, in the x-direction to align the facet 94 with the output fibre33.

[0070] The facet 64 of the faceted mirror 40 reflects the optical signaloutput by the input fibre 20 towards the point 78 on the common mirror16. The optical signal is incident on the point 78 of the common mirrorat an angle of incidence at which the common mirror reflects the opticalsignal towards the faceted mirror 53. At the faceted mirror 53, theoptical signal reflected by the common mirror is incident on the facet94, which is angled to reflect the optical signal into the output fibre33.

[0071] The method 100 according to the invention for switching anoptical signal received via an input optical path to an output opticalpath will now be described with reference to FIG. 9. The input opticalpath is any one of an array of M input optical paths. The output opticalpath is any one of an array of N output optical paths.

[0072] In process 102, an N-faceted mirror corresponding to each of theM input optical paths is provided.

[0073] In process 104, an M-faceted mirror corresponding to each of theN output optical paths is provided.

[0074] In process 106, each N-faceted mirror is located opposite the oneof the input optical paths to which it corresponds;

[0075] In process 108, each M-faceted mirror is located opposite the oneof the output optical paths to which it corresponds.

[0076] In process 110, the N-faceted mirror located opposite the inputoptical path is stepped to align one of its facets with the inputoptical path. The facet that is aligned with the input optical path isangled to reflect the optical signal towards the M-faceted mirrorlocated opposite the output optical path.

[0077] Finally, in process 112, the M-faceted mirror located oppositethe output optical path is stepped to align one of its facets with theoutput optical path. The facet that is aligned with the output opticalpath is angled to reflect light that would be received via the outputoptical path towards the N-faceted mirror located opposite the inputoptical path.

[0078] The method may additionally use the process described above withreference to FIG. 3A, for example, to change the output optical path towhich the optical signal received via the input optical path isswitched. The output optical path is changed from the output opticalpath referred to in FIG. 9, which will be called a first output opticalpath, to a second output optical path. The second output optical path isone of the output optical paths different from the first output opticalpath.

[0079] The method may additionally use the process described above withreference to FIGS. 4A and 4B, for example, to change the input opticalpath via which the optical signal is received from the input opticalpath referred to in FIG. 9, which will be called a first input opticalpath, to a second input optical path. The second input optical path isone of the input optical paths different from the first input opticalpath.

[0080] The invention has been described with reference to an example inwhich the 12 set of input optical paths and the set 14 of output opticalpaths are each composed of optical paths arranged in a one-dimensionalarray disposed in the x-direction. However, the optical paths in eitheror both of the set of input optical paths and the set of output opticalpaths may be arrayed in a one-dimensional array disposed in a directiondifferent from the x-direction, e.g., the z-direction. When the opticalpaths are arranged in a one-dimensional array disposed in thex-direction, the facets of the faceted mirrors are angled about thez-axis. When the optical paths are arranged in a one-dimensional arraydisposed in the z-direction, the facets of the faceted mirrors areangled about the x-axis. Regardless of the arrangement of the opticalpaths, the faceted mirror corresponding to each optical path is locatedopposite the optical path, as shown in FIGS. 1, 5 and 7.

[0081] As a further alternative, the optical paths in either or both ofthe set 12 of input optical paths and the set 14 of output optical pathsmay be arranged in a two-dimensional array. When the optical paths arearranged in a two-dimensional array, the faceted mirrors are alsoarranged in a two-dimensional array the faceted mirror corresponding toeach optical path located opposite each optical path, as shown in FIGS.1, 5 and 7. When the optical paths are arranged in a two-dimensionalarray, the facets of the faceted mirrors are angled about two axes. Forexample, the optical paths may be arranged in a two-dimensional arrayhaving rows parallel to the x-axis and columns parallel to the z-axis,with the facets of the faceted mirrors angled about the z-axis and thex-axis.

[0082] The invention has also been described with reference to anexample in which the faceted mirrors each comprise more than onereflective surface arrayed in the x-direction, as shown in FIG. 2A. Eachof the reflective surfaces provides one of the facets 61-64 of thefaceted mirror 40. The faceted mirrors may alternatively be configuredas shown in FIG. 2B. In this, the faceted mirror 40 comprises the singlereflective surface 65 shaped to provide the facets 61-64 arranged in aone-dimensional array in the x-y plane.

[0083] The invention has been described with reference to an example inwhich the facets of the faceted mirrors, such as the faceted mirror 40,are arranged in a one-dimensional array arrayed in the x-direction.However, the facets of the faceted mirrors may alternatively be arrayedin the x-z plane in a direction different from the x-direction. Forexample, the facets may be arrayed in the z-direction. In this case, themoving mechanism 70 preferably moves the faceted mirror in a directionparallel to that in which the facets are arrayed. For example, when thefacets are arrayed in the z-direction, the moving mechanism moves thefaceted mirror in the z-direction.

[0084] As a further alternative, the facets of the faceted mirrors maybe arranged in a two-dimensional array. For example, the facets may bearranged in a two-dimensional array having rows parallel to thex-direction and columns parallel to the z-direction. Specifically, thesingle reflective surface 65 shown in FIG. 2B may be shaped to providefacets arranged in a two-dimensional array that additionally extends inthe z-direction. As another example, a two-dimensional array of facetsmay be obtained by extending of the reflective surfaces shown at 61-64in FIG. 2A in the z-direction and dividing each of the reflectivesurfaces into a one-dimensional array of facets disposed in thez-direction.

[0085] In embodiments in which the facets of the faceted mirrors arearranged in a two-dimensional array, the moving mechanism 70 steps thestage 60 in two directions instead of the single direction shown inFIGS. 1 and 7. When the facets are arranged in a two-dimensional arrayhaving rows parallel to the x-direction and columns parallel to thez-direction, the moving mechanism steps the stage in the z-direction inaddition to the x-direction shown.

[0086] The invention has been described with reference to an example inwhich the facets, such as the facets 61-64, of the faceted mirrors haveflat surfaces. However, the facets can additionally be shaped to focusthe light reflected by the facet to optimize the coupling efficiencybetween the input optical path and the output optical path. Since theoptical path length between the input optical path and the outputoptical path that includes each facet differs, each facet is preferablyindividually shaped to focus the light reflected by the facet optimallyfor the length of the optical path in which the facet is located.

[0087] The precision of the angles of the facets of the faceted mirrorsdetermines the efficiency of the coupling between the input optical pathand the output optical path. The angle of each facet of each facetedmirror is determined once, when the optical switch is designed, and doesnot change during operation of the optical switch 10. Thus, the couplingefficiency of the optical switch is largely determined by the accuracywith which the faceted mirrors are designed and manufactured. The designprocess generates suitable tooling that is then used to mass-produce thefaceted mirrors at low cost and high repeatability. The faceted mirrors,or components of them, may be manufactured using mature andwell-controlled manufacturing processes. For example, the facetedmirrors, or components of them, may be manufactured from single-crystalsilicon by a micromachining process, or from a suitable plastic materialby molding. Similar processes can be used to make the moving mechanismof each faceted mirror.

[0088] Also affecting the coupling efficiency is the accuracy with whichthe facet of the faceted mirror is aligned with the input optical pathor the output optical path. The moving mechanism is required to step thefaceted mirror linearly in one or two directions, or rotationally, witha precision that ensures that only the facet that effects the desiredcoupling is aligned with the input optical path or the output opticalpath. The precision required of the moving mechanism is several ordersof magnitude less than that with which the angle of each mirror must bedynamically adjusted in at least one dimension in the conventionalMEMS-based optical switch. The angles of the faceted mirrors of theoptical switch according to the invention are pre-determined at thedesign stage and provide low-loss switching with easy mechanical controland long-term stability.

[0089] Although this disclosure describes illustrative embodiments ofthe invention in detail, it is to be understood that the invention isnot limited to the precise embodiments described, and that variousmodifications may be practiced within the scope of the invention definedby the appended claims.

We claim:
 1. An optical switch, comprising: optical paths organized intoa set of M input optical paths and a set of N output optical paths; afaceted mirror corresponding to each one of the M input optical paths,the faceted mirror including N facets; a faceted mirror corresponding toeach one of the N output optical paths, the faceted mirror including Mfacets; and a moving mechanism coupled to each faceted mirror to stepthe faceted mirror to selectively align one of the facets of the facetedmirror with the one of the optical paths to which the faceted mirrorcorresponds.
 2. The optical switch of claim 1, in which the facets ofeach of the faceted mirrors corresponding to one of the sets of theoptical paths are angled to reflect light towards a different one of thefaceted mirrors corresponding to the other of the sets of the opticalpaths.
 3. The optical switch of claim 1, in which: in one of the sets ofthe optical paths, the optical paths are arranged in a one-dimensionalarray; and the facets of the faceted mirror corresponding to each one ofthe optical paths in the one of the sets are angled about one axis. 4.The optical switch of claim 1, in which: in one of the sets of theoptical paths, the optical paths are arranged in a two-dimensionalarray; and the facets of the faceted mirror corresponding to each one ofthe optical paths is the one of the sets are angled about two axes. 5.The optical switch of claim 4, in which the axes are orthogonal to oneanother.
 6. The optical switch of claim 1, in which: the facets of thefaceted mirror are arranged in a one-dimensional array having an arraydirection; and the moving mechanism moves the faceted mirror in adirection parallel to the array direction.
 7. The optical switch ofclaim 6, in which the moving mechanism includes a linear electrostaticstepping motor.
 8. The optical switch of claim 1, in which: the facetsof the faceted mirror are arrayed in a two-dimensional array having twoarray directions; and the moving mechanism moves the faceted mirror intwo directions, each parallel to a different one of the arraydirections.
 9. The optical switch of claim 1, in which the movingmechanism includes a two-dimensional linear electrostatic steppingmotor.
 10. The optical switch of claim 1, in which the facets of thefaceted mirror are curved to focus light reflected by the facets. 11.The optical switch of claim 10, in which: light passes from one of theinput optical paths to one of the output optical paths via an opticalpath that includes one of the facets of the faceted mirror and whoseoptical path length depends on the identity of the one of the inputoptical paths and identity of the one of the output optical paths; andthe one of the facets is individually curved to focus the light in theoptical path in accordance with the optical path length thereof.
 12. Theoptical switch of claim 1, in which the moving mechanism steps thefaceted mirror linearly.
 13. The optical switch of claim 1, in which themoving mechanism steps the faceted mirror rotationally.
 14. The opticalswitch of claim 1, in which: the optical switch additionally comprises acommon mirror located between the input optical paths and the outputoptical paths and facing the faceted mirrors; and the facets of each ofthe faceted mirrors corresponding to one of the sets of the opticalpaths are angled to reflect light to be incident on the common mirror atangles of incidence at which the common mirror reflects the lighttowards a different one of the faceted mirrors corresponding to theother of the sets of the optical paths.
 15. A method for switching anoptical signal received via an input optical path to an output opticalpath, the input optical path being any one of an array of M inputoptical paths, the output optical path being any one of an array of Noutput optical paths, the method comprising: providing an N-facetedmirror corresponding to each one of the M input optical paths and anM-faceted mirror corresponding to each one of the N output opticalpaths; locating each N-faceted mirror opposite the corresponding one ofthe input optical paths; locating each M-faceted mirror opposite thecorresponding one of the output optical paths; stepping the N-facetedmirror corresponding to the input optical path to align one of thefacets thereof with the input optical path, the one of the facetsaligned with the input optical path being angled to reflect the opticalsignal towards the M-faceted mirror corresponding to the output opticalpath; and stepping the M-faceted mirror corresponding to the outputoptical path to align one of the facets thereof with the output opticalpath, the one of the facets aligned with the output path being angled toreflect light that would be received via the output optical path towardsthe N-faceted mirror corresponding to the input optical path.
 16. Themethod of claim 15, in which, in providing the N-faceted mirror and theM-faceted mirror, the facets of each of the faceted mirrorscorresponding to one of the sets of the optical paths are angled toreflect light towards a different one of the faceted mirrorscorresponding to the other of the sets of the optical paths.
 17. Themethod of claim 15, in which: the input optical path is a first inputoptical path; the method is additionally for changing the input opticalpath via which the optical signal is received from the first inputoptical path to a second input optical path, the second input opticalpath being one of the input optical paths different from the first inputoptical path; and the method additionally comprises: stepping theN-faceted mirror corresponding to the second input optical path to alignone of the facets thereof with the second input optical path, the one ofthe facets aligned with the second input optical path being angled toreflect the optical signal towards the M-faceted mirror corresponding tothe output optical path, and stepping the M-faceted mirror correspondingto the output optical path to align a different one of the facetsthereof with the output optical path, the different one of the facetsaligned with the output optical path being angled to reflect light thatwould be received via the output optical path towards the N-facetedmirror corresponding to the second input optical path.
 18. The method ofclaim 15, in which: the output optical path is a first output opticalpath; the method is additionally for changing the output optical path towhich the optical signal is switched from the first output optical pathto a second output optical path, the second output optical path beingone of the output optical paths different from the first output opticalpath; the method additionally comprises: stepping the N-faceted mirrorcorresponding to the input optical path to align a different one of thefacets thereof with the input optical path, the different one of thefacets aligned with the input optical path being angled to reflect theoptical signal towards the M-faceted mirror corresponding to the secondoutput optical path; and stepping the M-faceted mirror corresponding tothe second output optical path to align one of the facets thereof withthe second output optical path, the one of the facets aligned with thesecond output optical path being angled to reflect light that would bereceived via the second output optical path towards the N-faceted mirrorcorresponding to the input optical path.
 19. The method of claim 15, inwhich, in stepping the N-faceted mirror, the N-faceted mirror is steppedlinearly; and in stepping the M-faceted mirror, the M-faceted mirror isstepped linearly.
 20. The method of claim 15, in which, in stepping theN-faceted mirror, the N-faceted mirror is stepped rotationally; and instepping the M-faceted mirror, the M-faceted mirror is steppedrotationally.
 21. The method of claim 15, in which: the methodadditionally comprises: providing a common mirror, and locating thecommon mirror between the array of input optical paths and the array ofoutput optical paths, facing the faceted mirrors; and in providing theN-faceted mirror and the M-faceted mirror, the facets of each of thefaceted mirrors corresponding to one of the sets of the optical pathsare angled to reflect light to be incident on the common mirror atangles of incidence at which the common mirror reflects the lighttowards a different one of the faceted mirrors corresponding to theother of the sets of the optical paths.